The present invention relates to apparatus and methods for measuring the lateral dimensions of irradiated spacers of a nuclear fuel assembly and particularly relates to apparatus and methods for measuring the lateral dimensional envelope of irradiated spacers in fuel bundles while located within a nuclear reactor servicing pool to determine the extent of growth or out-of-squareness of the irradiated spacer.
Spacers are employed at axially spaced locations in fuel bundles to maintain the fuel rods separated from one another at well-defined lateral distances and permit flow of moderator/coolant from the lower tie plate of the nuclear fuel assembly upwardly through the assembly to generate steam ultimately used to produce electrical power. The fuel bundle comprising the spacers and fuel rods are encased within a generally rectangular fuel bundle channel and a plurality of such nuclear fuel assemblies makes up the core of a nuclear reactor. During operation in the nuclear reactor, the spacers in the nuclear fuel assemblies are subjected to radiation and thermomechanical stresses that can cause the overall dimensions of the spacers' envelopes to change, e.g., to increase. The term envelope as used herein means the lateral dimensions of the spacer, i.e., the X-Y dimensions, where the Z axis of the Cartesian coordinate system is in the direction of the fuel rods from the lower to the upper ends of the fuel bundle. If the envelope dimensions for a given spacer in a bundle increase to a significant extent, the ability to remove the fuel bundle from the channel and to reinsert the fuel bundle into a channel during servicing of the fuel assembly is seriously compromised. Accordingly, there is a need for a system for measuring the spacer envelope dimensions for each spacer in an irradiated or unirradiated assembled fuel bundle without requiring disassembly of the bundle and to enable the measurements to take place in situ in the nuclear reactor servicing pool.